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Abstract

Effects of an exotic tree legume on soil in farmland in the Ibadan area, southwestern Nigeria

U.E. Akpokodje and A.O. Aweto

An exotic tree legume, Gliricidia sepium, has become an established feature of agroforestry systems in southwestern Nigeria, especially in the Ibadan division, where it features prominently in cultivated fields and fallow land. The effect of the tree on soil properties has been studied in alley cropping systems but not in native farmers’ fields in southwestern Nigeria. The present study examines the effects of Gliricidia sepium on the properties of soil underneath its canopy in continuously cultivated farmlands in the peri-urban zone of Ibadan, southwestern Nigeria. It also seeks to find out whether the effects of the tree on the soil differ on soil derived from granite, quartzite and gneiss under the same type of traditional farming. In contrast to the findings reported in the literature for the tree in alley farming systems, Gliricidia sepium was not observed to significantly improve soil organic matter, exchangeable cations and CEC under its canopy, compared with soil outside its canopy in the farmers’ fields. Similarly, there was no significant build-up of the extractable

micronutrients – iron, copper, manganese and zinc – under the tree canopy. There was no significant build-up of organic matter and nutrients in soil underneath the tree canopy, due to frequent cultivation and the burning of the vegetation slash and crop residue prior to cultivation. The effect of Gliricidia sepium is similar on the two types of soil.